1. Field of the Invention
The present invention relates to an information reading and recording device, for reading and recording information as an optical signal, which comprises a reading or recording head of an optical disk device, or optical magnetic disk device, used as a storage device for a computer.
In accordance with the development of high performance computers, it has become necessary to incorporate a storage device of large capacity into the computer. As the storage device to be incorporated into the computer, attention is given to a hard disk device and an optical disk device. Especially, the latter is advantageous in that the disk medium can be easily attached to and detached from the computer, that is, the disk medium can be easily replaced and further the capacity of the disk medium is large and the device is compact and the weight is small. For the above reasons, the optical disk device has become important.
2. Description of the Related Art
It is necessary to further reduce the price of an optical disk device or optical magnetic disk device. In order to reduce the price, there is a strong demand for reducing the price of an optical head portion. Therefore, it has been conventionally necessary to provide a system in which the number of parts of an optical head can be decreased and the size and weight of the optical head can be reduced and also the labor to adjust the optical head can be reduced. On the other hand, in a disk medium in which both reading and recording of data can be conducted, there is a strong demand for increasing the luminous energy of laser beams, and also there is a strong demand for increasing the quantity of light for servo detection or the transmission of an information signal.
For the above reasons, reduction of the number of parts, reduction of labor for adjustment and reduction of the size and weight, by integrating a large number of optical elements such as a polarization separating element of a polarization beam splitter or Wollaston prism, a beam splitter and a mirror into one package, are strongly required.
FIG. 1 is a view showing a signal detection optical system used for a conventional optical head of an optical magnetic disk. Laser beam emitted from a semiconductor laser 1, which is a light source, is made parallel by a collimator lens 2. After a portion of the parallel beam has been transmitted through a beam formation prism 3, it is directed to an optical magnetic disk, which is a storage medium, by a polarization beam splitter 4 and condensed onto an optical magnetic disk 6 by an objective lens 5.
When written data exists on the optical magnetic disk 6, an angle of polarization of light is rotated by the Kerr effect. That is, when written data exists on the optical magnetic disk 6, laser beams of P-polarization light component used for detection are rotated by an angle of xcex8k by the Kerr effect. Therefore, a small quantity of S-polarization light component is generated. Polarization light components (S-component and P-component) of the rays which have returned from the optical magnetic disk 6 are reflected on the polarization beam splitter 4. A beam of light, which has been reflected by the polarization beam splitter 4, is reflected by the polarization beam splitter 7. Then, the beam of light passes through xc2xd wave plate 8 and condenser lens 9. After that, the beam of light is separated into an S-polarization light component and a P-polarization light component by the polarization light beam splitter 10.
The S-polarization light component and the P-polarization light component are respectively incident on the light detectors 11, 12. When a difference in the intensity of these two signals is found, it is possible to detect a signal.
On the other hand, polarization light components of the rays which have returned from the optical magnetic disk 6 are reflected on the polarization beam splitter 4. A portion of the beam of light, which has been reflected on the polarization beam splitter 4, is reflected on the polarization beam splitter 7 and transmitted through the condenser lens 13. Then, the beam of light is incident on the beam splitter 14. After that, focus is detected by the push-pull method in which the knife edge 15 and the optical detector 16 are used, and the track is detected by an optical detector 17.
As described above, in a conventional signal detection optical system of the optical head for the optical magnetic disk shown in FIG. 1, it is necessary to provide a large number of optical elements such as a polarization separating element of a polarization beam splitter or Wollaston prism, a beam splitter and a mirror. When these optical elements are incorporated, it is necessary to provide a large amount of labor for adjusting these optical elements.
In order to simplify the above-mentioned optical system, as shown in FIG. 2, a structure is proposed in which a servo detection optical system is integrated with a semiconductor laser using a diffraction grating element such as a hologram. That is, in FIG. 2, the optical system 20 of the optical head includes a semiconductor laser 21, a hologram 23 for conducting tracking and detection of the focus, and an optical detection element 24, which are integrated with each other.
The hologram 23 has a plurality of hologram regions 23a to 23d. Reference numerals 23a, 23b are hologram regions for the focus servo, and reference numerals 23c, 23d are hologram regions for the tracking servo. There are provided optical detection elements 24a to 24d for detecting beams of light which have diffracted in the hologram regions 23a to 23d. Reference numerals 24a, 24b are optical detection elements for detecting a focus error signal (FES), and reference numerals 24c, 24d are optical detection elements for detecting a tracking error signal (TES). When the above structure is employed, the optical system can be made compact and simple.
However, even if the above optical system is used, in order to provide a sufficient margin, it is necessary to increase the quantity of light of the laser beams on the overwriting medium. However, an increase in the quantity of light of the laser beams is restricted by a limitation in the manufacture of semiconductor lasers.
In the above optical head used for an optical magnetic disk, in the beam splitter or hologram, when an efficiency of the returning process is lowered in which servo detection of the focus error and tracking error is conducted, it is possible to enhance an efficiency of the outgoing process which is directed to the optical disk medium. However, the above method has a problem in which a quantity of light for servo detection is lowered. For example, when a transmission factor in the outgoing process is 90% in the beam splitter, a reflection factor in the returning process is lowered to 10%. Therefore, it is necessary to enhance the efficiency in the outgoing process.
It is an object of the present invention to greatly reduce the number of parts and the labor required for adjustment by incorporating parts, which are integrated with each other, into one body together with the package of a semiconductor laser without using a large number of optical elements such as a polarization beam splitter (polarization beam splitter, Wollaston prism and so forth), a beam splitter and a mirror.
Also, it is an object of the present invention to easily realize overwriting when the quantity of light of a servo is distributed to the outgoing process and the returning process in such a manner that the distribution of a quantity of light is changed in accordance with the reading on recording mode.
The present invention provides an optical signal information reading and recording device comprising: a semiconductor laser used as a light source; an image formation lens for condensing a beam of light sent from the semiconductor laser so as to form an image on an optical disk medium; a diffraction optical element for detecting a signal of the optical disk medium, arranged on an optical path between the semiconductor laser and the image formation lens; and a signal detection optical system for detecting a beam of light diffracted by the diffraction optical element; the optical signal information reading and recording device further comprising a polarization light changeover element arranged between the semiconductor laser and the diffraction optical element, wherein a polarization direction of light is changed so that a transmission factor of the diffraction optical element can be higher than the diffraction efficiency in the case of recording conducted on the disk medium by laser beams and a transmission factor of the diffraction optical element can be lower than the diffraction efficiency in the case of recording conducted on the disk medium by laser beams.
According to a further aspect of the present invention, there is provided an optical signal information reading and recording device comprising: an optical source; a lens arranged between the optical source and an optical recording medium for condensing a light emitted from the optical source on the optical recording medium; a diffraction optical element arranged between the optical source and the optical recording medium; a polarization light changeover element for changing a polarization direction of the light emitted from the optical source, wherein the polarization direction of the light emitted from the optical source is changed between in the case of reading information recorded in the optical recording medium and in the case of recording information to the optical recording medium.
In the present invention, the efficiency (transmission efficiency and diffraction efficiency) is changed in the outgoing process and the returning process. That is, in the case of recording, beams of light are transmitted in the diffraction optical grating by a transmission factor of 90% when overwriting is conducted on a medium. At this time, the diffraction efficiency becomes 10% at maximum, however, the quantity of light on the medium is large. Therefore, a quantity of light which has returned after being reflected is sufficiently large. For this reason, even if the diffraction efficiency is 10%, it is possible to conduct a sufficient detection of the quantity of light.
Next, in the case of reading, it is sufficient that a transmission factor of the diffraction optical element is 10%. The reason is that there is a possibility of recording when a quantity of light on the medium is large. However, it is necessary that the quantity of detected light for reading is large. Since this diffraction efficiency is 90% at maximum, it is possible to detect a sufficiently large quantity of light in the servo detection.
The polarization light changeover element is a liquid crystal element for changing over a polarization direction of light arranged on an optical path between the semiconductor laser and the diffraction optical element, and the voltage on the liquid crystal element is controlled so as to set a polarization direction of light so that a transmission factor of the diffraction optical element can be maximum in the case of recording and also the voltage on the liquid crystal element is controlled so as to set a polarization direction of light so that a diffraction efficiency of the diffraction optical element can be maximum in the case of reading. In this case, the changeover can be conducted by only controlling voltage and without moving the liquid crystal element.
The polarization light changeover element is a xc2xd wave plate for rotating a direction of polarization of light, which is arranged between the semiconductor laser and the diffraction optical element, the direction of the optical axis of the wave plate is set at a polarization direction of light in which a transmission factor of the diffraction optical element becomes maximum in the case of recording, the polarization direction of light is set so that the transmission factor of the diffraction optical element can be maximum in the case of recording when the wave plate is provided, the polarization direction of light is set so that the transmission factor of the diffraction optical element can be maximum in the case of reading when a wave plate is not provided, and the xc2xd wave plate is moved so that it can be taken in and out with respect to the optical axis in the recording and reading modes.
The diffraction optical element is formed in such a manner that a diffraction grating is provided in a double refraction optical element.
A diffraction pattern for conducting tracking detection and focus detection is formed on the diffraction optical element, and the diffraction optical element, polarization of light changeover element, semiconductor laser and optical detection element are integrated into one body being packaged.